Department of Paleontology, Universidad de la República, Montevideo, Uruguay.
Servicio Académico Universitario y Centro de Estudio Paleontológicos (SAUCE-P), Universidad de la República, Sauce, Canelones, Uruguay.
PeerJ. 2024 Aug 7;12:e17815. doi: 10.7717/peerj.17815. eCollection 2024.
Nutrient foramina are small openings in the periosteal surface of the mid-shaft region of long bones that traverse the cortical layer and reach the medullary cavity. They are important for the delivery of nutrients and oxygen to bone tissue and are crucial for the repair and remodeling of bones over time. The nutrient foramina in the femur's diaphysis are related to the energetic needs of the femur and have been shown to be related to the maximum metabolic rate (MMR) of taxa. Here, we investigate the relationship between nutrient foramen size and body mass as a proxy to the aerobic capacity of taxa in living and extinct xenarthrans, including living sloths, anteaters, and armadillos, as well as extinct xenarthrans such as glyptodonts, pampatheres, and ground sloths. Seventy femora were sampled, including 20 from extant taxa and 50 from extinct taxa. We obtained the blood flow rate (Q̇) based on foramina area and performed PGLS and phylogenetic ANCOVA in order to explore differences among mammalian groups. Our results show that, among mammals, taxa commonly associated with lower metabolism like living xenarthrans showed relatively smaller foramina, while the foramina of giant extinct xenarthrans like ground sloths and glyptodonts overlapped with non-xenarthran placentals. Consequently, Q̇ estimations indicated aerobic capacities comparable to other placental giant taxa like elephants or some ungulates. Furthermore, the estimation of the MMR for fossil giant taxa showed similar results, with almost all taxa showing high values except for those for which strong semi-arboreal or fossorial habits have been proposed. Moreover, the results are compatible with the diets predicted for extinct taxa, which indicate a strong consumption of grass similar to ungulates and in contrast to the folivorous or insectivorous diets of extant xenarthrans. The ancestral reconstruction of the MMR values indicated a lack of a common pattern for all xenarthrans, strongly supporting the occurrence of low metabolic rates in extant forms due to their particular dietary preferences and arboreal or fossorial habits. Our results highlight the importance of considering different evidence beyond the phylogenetic position of extinct taxa, especially when extinct forms are exceptionally different from their extant relatives. Future studies evaluating the energetic needs of giant extinct xenarthrans should not assume lower metabolic rates for these extinct animals based solely on their phylogenetic position and the observations on their extant relatives.
营养孔是长骨骨干中段骨膜表面的小开口，穿过皮质层到达骨髓腔。它们对骨组织的营养物质和氧气的输送很重要，对于骨骼的修复和重塑随着时间的推移至关重要。股骨骨干中的营养孔与股骨的能量需求有关，并已证明与分类群的最大代谢率（MMR）有关。在这里，我们研究了营养孔大小与身体质量之间的关系，以作为生活和已灭绝的有袋动物（包括现存的树懒、食蚁兽和犰狳）以及已灭绝的有袋动物（如雕齿兽、袋熊和地懒）的分类群有氧能力的替代指标。我们采样了 70 根股骨，其中包括 20 根来自现存分类群和 50 根来自已灭绝分类群。我们根据孔面积获得了血流率（Q̇），并进行了 PGLS 和系统发育协方差分析，以探索哺乳动物群体之间的差异。我们的结果表明，在哺乳动物中，与代谢率较低相关的常见分类群，如现存的有袋动物，其营养孔相对较小，而地懒和雕齿兽等巨型已灭绝的有袋动物的营养孔则与非有袋类胎盘动物重叠。因此，Q̇估计表明有氧能力与大象或其他一些有蹄类动物等其他胎盘类巨型分类群相当。此外，对化石巨型分类群的 MMR 估计也得到了类似的结果，除了那些被认为具有强烈半树栖或穴居习性的分类群外，几乎所有分类群的 MMR 都很高。此外，结果与为已灭绝分类群预测的饮食相符，这表明它们强烈地消耗类似于有蹄类动物的草，而与现存的有袋动物的食草或食虫饮食形成对比。MMR 值的祖先重建表明，所有有袋动物都没有一个共同的模式，这强烈支持了现存形式由于其特殊的饮食偏好和树栖或穴居习性而导致代谢率较低的观点。我们的研究结果强调了在考虑已灭绝分类群的系统发育位置之外，考虑不同证据的重要性，特别是当已灭绝的形式与其现存的亲属明显不同时。未来评估巨型已灭绝有袋动物能量需求的研究不应该仅根据它们的系统发育位置和对现存亲属的观察来假设这些已灭绝动物的代谢率较低。
